MILIOLIDA. | 2] 
Characters.— Shell ear-shaped, reniform, or orbicular, compressed, thickened at the 
umbilicus. Chambers arranged spirally, usually divided into chamberlets. Pseu- 
dopodial orifices in one or more rows on the peripheral edge of the last chamber. 
Surface of the chamber frequently marked by delicate parallel transverse riblets. 
Diameter, 3th to ith inch. 
Orbiculina flourishes in warm seas, but seems to be very rare in the Mediterranean. 
It is sparingly found in some of the European Tertiaries. Only one specimen, small and 
reniform, has occurred to us from the Crag (Sutton ?). 
2. OrsicuLina compressa, D’Orbigny. Plate IU, fig. 43. 
OrpicuLina compressa, D’Oré., 1840. Foram. Cuba, p. 66, pl. 8, figs. 4—7. 
OrBITOLITES CoscINoDIscus, S. Wood, 1843. Morris’s Cat. Brit. Foss., p. 42; 1844, Mag. 
N. Hist., vol. xiii, p. 21. 
— (2) — Id. 1854. Morris’s Cat. Brit. Foss., 2nd edit., p. 39. 
Characters.—Shell complanate, discoidal. Earlier chambers arranged spirally, as in 
the type, later chambers cyclical. Chambers subdivided into chamberlets. 
Diameter, ?th inch. 
Although in localities where Ordzculine are plentiful, specimens of a large size are 
often found retaining the spiral arrangement throughout their whole series of chambers, 
we more frequently find that those which attain the finest proportions have assumed an 
outspread discoidal form, in place of the ear-like or reniform shape, owing to the 
alteration in the plan of development before alluded to. When this change commences, 
as is often the case after a very few chambers have been formed, a thickening of the 
umbilicus is almost the only external character which will enable us to separate the speci- 
mens from those of the closely allied genus Ordztolites, and even this feature may be 
wanting. Microscopical examination of the central or umbilical portion of the disk 
usually yields a ready means of determining the affinities of doubtful specimens in the 
arrangement of the early chambers. Ordiculina has invariably a nucleus of spirally 
arranged segments, however large and ouispread the finely grown specimen may be; 
whilst Ordctolites, commencing growth with one or two large chambers, is built up entirely 
of concentric bands, in even the smallest and most obscure examples. 
Specimens of O. compressa were not rare in the Crag at Sutton some years ago, 
when worked at by Mr. Wood. The figured specimen is of large size, but somewhat 
worn and broken. 
Mr. Wood, in his “Catalogue of the Zoophytes from the Crag,” ‘Mag. Nat. Hist.,’ 
1844, vol. xiii, p. 21, describes, under the name of Orditolites coscinodiscus, some 
specimens of this Foraminifer obtained at Ramsholt and Sutton. It is there stated that 
